The first hypothesis to be experimentally explored in this project states that the systemic enhancement of complete carcinogenesis by previous UV irradiation can result from increased DNA adduct levels in carcinogen- targeted tissue, and/or from inhibition of secretion of the cytokines interferon-gamma and interleukin-2, which stimulate T helper one lymphocytes. the second hypothesis states that the systemic prevention of tumor promotion by previous UV irradiation results from UV-induced changes in the genetic and/or physiological responses to TPA. The specific aims to approach these hypotheses include: 1) to evaluate the ability of dorsal UV irradiation to systemically influence the carcinogen-induced levels of DNA adducts over time (21 days) after exposure to the direct acting N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) or to the indirect acting benzo[a]pyrene (BP); 2) to assess the influence of dorsal UV irradiation on selected parameters of ventral tumor promotion (PKC activation, hyperplasia, induction of TPA-inducible genes); and 3) to assess the roles of specific cytokines (IFN-gamma, interleukins-2, -4, -10) in UV regulation of antigenic BP-induced tumor rejection. In the first specific aim, the levels of O6-methylguanine and N7-methylguanine in ventral epidermal DNA of previously dorsally UVB irradiated mice after ventral exposure to MNNG will be measured. Levels of epidermal DNA adducts after ventral exposure to the ultimate carcinogen anti-[3H]benzo[a]pyrene-7,8-diol-9,10-epoxide versus the procarcinogen [3H]BP will be measured. The rate of disappearance of labeled BP-DNA adducts will be compared with that of prelabelled DNA from ventral epidermis in dorsally UV irradiated and unirradiated mice. In the second specific aim, PKC activation, histological hyperplasia, and the genetic expression of metallothionein IIA, c-jun, c-fos, c-myc, p53, and stromelysin will be measured in ventral epidermis with and without ventral TPA treatment in dorsally UV irradiated mice. In specific aim #3, the ability of cells from lymph nodes draining BP-induced tumor implants to secrete INF-gamma, IL-2, IL-4 and IL-10 upon in vitro exposure to the tumor antigens will be measured in UV irradiated and unirradiated mice. Additionally, functional roles of these cytokines in UV-induced immunosuppression will be tested by modulating the level of these cytokines in a passive transfer assay for immunosuppression. By defining the extent and mechanisms by which UV irradiation modulates host resistance to chemical carcinogenesis, new strategies for tumor prevention can be devised.